Method and system for service group management in a cable network

ABSTRACT

A cable modem termination system (CMTS) may determine, for a plurality of cable modems served by the CMTS, a corresponding plurality of SNR-related metrics. The CMTS may assigning the modems among a plurality of service groups based on the SNR-related metrics. For any one of the modems, the CMTS may configure physical layer communication parameters to be used by the one of the modems based on a SNR-related metric of a service group to which the one of the modems is assigned. The physical layer communication parameters may include one or more of: transmit power, receive sensitivity, timeslot duration, modulation type, modulation order, forward error correction (FEC) type, and FEC code rate. The CMTS and the modems may communicate using orthogonal frequency division multiplexing (OFDM) over a plurality of subcarriers, and the physical layer communication parameters may be determined on a per-subcarrier basis.

PRIORITY CLAIM

This patent application is a continuation of U.S. patent applicationSer. No. 13/948,444 filed on Jul. 23, 2013, which makes reference to,claims priority to and claims benefit from U.S. Provisional PatentApplication Ser. No. 61/674,742 titled “Method and System for ServiceGroup Management in a Cable Television Network” and filed on Jul. 23,2012.

The entirety of each of the above-mentioned applications is herebyincorporated herein by reference.

INCORPORATION BY REFERENCE

This application also makes reference to:

-   U.S. patent application Ser. No. 13/553,328 titled “Method and    System for Client-Side Message Handling in a Low-Power Wide Area    Network,” and filed on Jul. 19, 2012;-   U.S. patent application Ser. No. 13/485,034 titled “Method and    System for Server-Side Message Handling in a Low-Power Wide Area    Network,” and filed on May 31, 2012;-   U.S. patent application Ser. No. 13/553,175 titled “Method and    System for a Low-Power Client in a Wide Area Network,” and filed on    Jul. 19, 2012;-   U.S. patent application Ser. No. 13/553,195 titled “Method and    System for Server-Side Handling of a Low-Power Client in a Wide Area    Network,” and filed on Jul. 19, 2012;-   U.S. patent application Ser. No. 13/948,401 titled “Method and    System for a High Capacity Cable Network,” and filed on the same    date as this application; and-   U.S. patent application Ser. No. 13/948,417 titled “Method and    System for Noise Suppression in a Cable Network,” and filed on the    same date as this application.

The entirety of each of the above-mentioned applications is herebyincorporated herein by reference.

FIELD OF THE INVENTION

Certain embodiments of the invention relate to cable televisionnetworks. More specifically, certain embodiments of the invention relateto a method and system for service group management in a cabletelevision network.

BACKGROUND OF THE INVENTION

Convention cable television networks can be inefficient and haveinsufficient capacity. Further limitations and disadvantages ofconventional and traditional approaches will become apparent to one ofskill in the art, through comparison of such systems with some aspectsof the present invention as set forth in the remainder of the presentapplication with reference to the drawings.

BRIEF SUMMARY OF THE INVENTION

A system and/or method is provided for service group management in acable television network, substantially as shown in and/or described inconnection with at least one of the figures, as set forth morecompletely in the claims.

These and other advantages, aspects and novel features of the presentinvention, as well as details of an illustrated embodiment thereof, willbe more fully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram of an example cable/DOCSIS network.

FIG. 2A depicts an example method of determining locations of CMs withinthe HFC network.

FIGS. 2B and 2C depict signal-to-noise ratio (SNR) versus frequencyprofiles for an example cable/DOCSIS network.

FIG. 3A is a flowchart illustrating an example process for configuring acable/DOCSIS HFC network based on measured performance metrics.

FIG. 3B is a flowchart illustrating an example process for configuring acable/DOCSIS HFC network based on location of CMs within the network.

FIGS. 4A and 4B illustrate the network of FIG. 1, with differentgroupings of CMs based on one or both of: measured performance metric(s)and location within the HFC network.

DETAILED DESCRIPTION OF THE INVENTION

As utilized herein the terms “circuits” and “circuitry” refer tophysical electronic components (i.e. hardware) and any software and/orfirmware (“code”) which may configure the hardware, be executed by thehardware, and or otherwise be associated with the hardware. As usedherein, for example, a particular processor and memory may comprise afirst “circuit” when executing a first one or more lines of code and maycomprise a second “circuit” when executing a second one or more lines ofcode. As utilized herein, “and/or” means any one or more of the items inthe list joined by “and/or”. As an example, “x and/or y” means anyelement of the three-element set {(x), (y), (x, y)}. As another example,“x, y, and/or z” means any element of the seven-element set {(x), (y),(z), (x, y), (x, z), (y, z), (x, y, z)}. As utilized herein, the term“exemplary” means serving as a non-limiting example, instance, orillustration. As utilized herein, the terms “e.g.,” and “for example”set off lists of one or more non-limiting examples, instances, orillustrations. As utilized herein, circuitry is “operable” to perform afunction whenever the circuitry comprises the necessary hardware andcode (if any is necessary) to perform the function, regardless ofwhether performance of the function is disabled, or not enabled, by someuser-configurable setting.

FIG. 1 is a diagram of an example cable/DOCSIS network. The examplenetwork comprises a cable modem termination system (CMTS) 102, a fibernode 104, amplifiers 106 ₁-106 ₃, a directional coupler 108, splitters110 ₁-110 ₃, and cable modems (CMs) 112 ₁-112 ₅.

The CMTS 102 may comprise circuitry operable to manage connections tothe CMs 112 ₁-112 ₅. This may include, for example: participating inranging operations to determine physical layer parameters used forcommunications between the CMTS 102 and CMs 112 ₁-112 ₅; forwarding ofdynamic host configuration protocol (DHCP) messages between a DHCPserver and the CMs 112 ₁-112 ₅; forwarding of time of day messagesbetween a time of day server and the CMs 112 ₁-112 ₅; directing trafficbetween the CMs 112 ₁-112 ₅ other network devices (e.g., Ethernetinterfaces of the CMTS 102 may face the Internet, Optical RF interfacesof the CMTS 102 may face the CMs, and the CMTS may direct trafficbetween and among the Ethernet and Optical RF interfaces); and managingregistration of the CMs 112 ₁-112 ₅ to grant the cable modems network(e.g., Internet) access. The registration process for a CM 112 _(X) (Xbetween 1 and 5 for the example network of FIG. 1) may comprise the CM112 sending a registration request along with its configurationsettings, and the CMTS 102 accepting or rejecting the cable modem basedon the configuration settings. The registration process may additionallycomprise an exchange of security keys, certificates, or otherauthentication information.

The fiber node 104 may comprise circuitry operable to convert betweenoptical signals conveyed via the fiber optic cable 103 and electricalsignals conveyed via coaxial cable 105.

Each of the amplifiers 106 ₁-106 ₃ may comprise a bidirectionalamplifier which may amplify downstream signals and upstream signals,where downstream signals are input via upstream interface 107 a andoutput via downstream interface 107 b, and upstream signals are inputvia downstream interface 107 b and output via upstream interface 107 a.The amplifiers 106 ₁, which amplifies signals along the main coaxial“trunk” may be referred to as a “trunk amplifier.” The amplifiers 1062and 1063 which amplify signals along “branches” split off from the trunkmay be referred to as “branch” or “distribution” amplifiers.

The directional coupler 108 may comprise circuitry operable to directdownstream traffic incident on interface 109 a onto interfaces 109 b and109 c, and to direct upstream traffic incident on interfaces 109 b and109 c onto interface 109 a. The directional coupler 108 may be a passivedevice.

Each of the splitters 110 ₁-110 ₃ may comprise circuitry operable tooutput signals incident on each of its interfaces onto each of its otherinterfaces. Each of the splitters 110 ₁-110 ₃ may be a passive device.

Each of the cable modems (CMs) 112 ₁-112 ₅ may comprise circuitryoperable to communicate with, and be managed by, the CMTS 1102 inaccordance with one or more standards (e.g., DOCSIS). Each of the CMs112 ₁-112 ₅ may reside at the premises of a cable subscriber.

The components (including, fiber optic cables, coaxial cables,amplifiers, directional couplers, splitters, and/or other devices)between the CMTS and the CMs may be referred to as a hybrid fibercoaxial (HFC) network. Any of the amplifiers, directional coupler, andsplitters may be referred to generically as a coupling device.

FIG. 2A depicts an example method of determining locations of CMs withinthe HFC network. As shown in FIG. 2A, to determine one or more measuredperformance metric(s) (e.g., an SNR-related metric such as SNR at aparticular frequency or SNR over a range of frequencies (an SNRprofile), noise levels, strength of desired signals, and/or the like)for any particular CM 112 _(X), the CMTS 102 may transmit, at time 1, amessage 202 that is destined (unicast, multicast, or broadcast) for theCM 112 _(X) and that functions as a probe to enable determination of themetric(s) for the CM 112 _(X). The message 202 may be sent on multiplechannels spanning multiple frequencies. Similarly, where OFDM is usedfor communications between the CMTS 102 and the CM 112 _(X), the message202 may be transmitted on each subcarrier, or may be sent on a subset ofsubcarriers and then interpolation may be used for determining the SNRof subcarriers on which the message 202 was not sent.

The message 202 may be transmitted with such encoding, modulation, andtransmit power such that even a CM 112 _(X) with a worst-caseperformance metric(s) can receive the message and accurately measure themetric(s). In this regard, FIG. 2B shows a SNR versus frequency graphfor an example HFC network that uses eight channels/subcarriers. Theline 222 in FIG. 2B represents a composite worst-case SNR profile forone or more CM(s) in the HFC network to which the message 202 isdestined. For example, line 222 may be a SNR profile for a single CM 112_(X) to which the message 202 is to be unicast. As another example, theline 222 may be a composite worst-case SNR profile for a plurality ofCMs 112 of a particular service group to which the message 202 is to bemulticast. As another example, the line 222 may be a compositeworst-case SNR profile for all CMs of an HFC network handled by the CMTS102 to which the message 202 is to be broadcast. The message 202 may betransmitted such that the minimum SNR needed to receive and accuratelymeasure the SNR profile is below the line 222 (e.g., SNR needed forreceiving the message 202 may be the line 224).

Upon receipt of the message 202, a CM 112 _(X) may measure, over thechannels/subbands on which the message was sent, one or more metrics(e.g., SNR versus frequency profile) for the transmission 202. The CM112 _(X) may then report the metrics(s) back to the CMTS 102 via amessage 204. In an example implementation, the message 202 may containinformation about when and/or how the CM(s) are supposed to report theirmetric(s) (e.g., SNR profiles) back to the CMTS 102. In this regard, themessage 202 may contain information that is the same as and/or oranalogous to what may be found in a MAP, UCD, and/or other MACmanagement message defined in a DOCSIS standard. Accordingly, themessage 202 may have specified a format of the message 204 and that themessage 204 is to be transmitted at time T+Δ.

Once the metric(s) of one or more CMs are known to the CMTS 102,physical layer communication parameters to be used for communicationsbetween the CMTS 102 and the CMs 112 may be determined based on themetric(s). In this regard, physical layer communication parameters maybe determined per-CM based on each CM's respective metric(s) (e.g., eachCM's SNR profile), per-service-group based on a composite metric(s) ofthe CM(s) assigned to that service group (e.g., composite SNR profilefor the CM(s) of that service group), per physical region of the HFCnetwork based on a composite metric of the CMs located in that physicalregion (e.g., composite SNR profile for the CM(s) in that physicalregion), and/or the like. Furthermore, once the metric(s) of a CM 112_(X) is determined, the CMTS 102 may assign that CM 112 _(X) to one ormore service groups based on its metric(s), as, for example, describedbelow with reference to FIG. 4A. Example physical layer parametersinclude: encoding parameters, modulation parameters, transmit power,receive sensitivity, timeslot duration, channel(s) or subcarrier(s) onwhich to listen, channel(s) or subcarrier(s) on which to transmit,and/or the like. Example encoding parameters include: type of forwarderror correction (FEC) to be used (e.g., Reed-Solomon, LDPC, etc.), FECblock size, FEC code rate, etc. Example modulation parameters include:type of modulation (e.g., frequency shift keying (FSK), phase shiftkeying (PSK), quadrature amplitude modulation (QAM), etc.), modulationdepth, modulation order, etc.

In an example implementation, the transmission of messages 202, thecalculation of metrics, such as SNR profile, by the CM(s), thetransmission 204, and subsequent configuration of physical layerparameters based on the metric(s) may take place in parallel with otheroperations performed during the registration/ranging process.

Referring now to FIG. 2C, there is again shown the line 222 whichrepresents the applicable SNR profile (e.g., an individual SNR profileif configuring physical layer parameters per CM, a composite SNR profilefor a service group if configuring physical layer parameters per servicegroup, or a composite SNR profile for a particular physical region).Also shown is a line 226 corresponding to SNR utilization forcommunications with the CM(s) associated with the profile 222. Assumingthe distance 228 is the minimum desired headroom, then the physicallayer communication parameters resulting in line 226 are nearly optimalin the sense that there is minimal headroom on each of channels/subbands1, 3, 4, 6, 7, 8, and only slightly more than minimal headroom onchannels/subbands 2 and 5.

Physical layer parameters may be configured/coordinated using upstreamand/or downstream MAP messages, upstream channel descriptors (UCDs),other MAC management messages defined in DOCSIS protocols, and/orpurpose-specific messages tailored to configuring the parameters basedon measured performance metrics such as SNR profiles as described inthis disclosure.

FIG. 3A is a flowchart illustrating an example process for configuring acable/DOCSIS HFC network based on SNR profiles. For clarity ofillustration the process is described with reference to the network ofFIG. 1 and the messages of FIG. 2A. The process begins with block 302 inwhich the CMTS 102 sends one or more probe messages 202 to the CMs 112₁-112 ₅. In block 304, each of the CMs 112 ₁-112 ₅ determines itsrespective SNR profile based on a received one of the messages 202, andreports the SNR profile back to the CMTS 102 in the form of a message204. In block 306, the CMTS 102 assigns the CMs to service groups basedon the SNR profiles.

In block 308, physical layer communication parameters are determined perservice group and per channel/subcarrier. For example, for anyparticular service group, the modulation order and FEC code rate to beused on a particular subcarrier may be determined based on the worstcase SNR for that subcarrier among the CMs in that particular servicegroup. Thus, it can be seen that grouping CMs based on SNR profiles mayenable configuring physical layer communications parameters to such thatone or more communication parameters (throughput, reliability, etc.) isoptimal, or near-optimal, for all of the CMs in the service group. Forexample, without such grouping by SNR profile, one CM in a particularservice group may have substantially lower SNR on one or morechannels/subcarriers. As a result, all CMs in that particular servicegroup may be forced to use physical layer parameters supported by this“lowest common denominator” CM. This may result in a lot of wastedcapacity for the remaining CMs.

To illustrate with a specific example: assume that CMs 112 ₁, 112 ₄, and112 ₅ of FIG. 1 have sufficient SNR on channel z to support 64-QAM onchannel z, but that CMs 112 ₂ and 112 ₃ only have sufficient SNR onchannel z to support 16-QAM. If 112 ₁ is assigned to the same servicegroup as 112 ₂ or 112 ₃, then 112₁ may be forced to use 16-QAM onchannel z. Conversely, if 112 ₁, 112 ₄, and 112 ₅ are assigned to afirst service group and 112 ₂ and 112 ₃ are assigned to a second servicegroup, then the first service group consisting of 112 ₁, 112 ₄, and 112₅ can use 64-QAM on channel z while the second service group consistingof 112 ₂ and 112 ₃ uses 16-QAM on channel z.

In block 310, communications between the CMTS 102 and any particularservice group use the per-service-group and per-subcarrier/channelphysical layer parameters determined in block 308.

FIG. 3B is a flowchart illustrating an example process for configuring acable/DOCSIS HFC network based on location of CMs within the network.For clarity of illustration, and as a non-limiting example, the processis described with reference to the network of FIG. 1 and the messages ofFIG. 2B. The process begins with block 322 in which the CMTS 102determines a location of each of the CMs 112 ₁-112 ₅ in the network.Location of a CM 112 _(X) may be characterized in a variety of waysincluding, for example: total distance of fiber and/or coaxial cablebetween the CMTS 102 and the CM 112 _(X), total attenuation between theCMTS 102 and the CM 112 _(X), which trunk amplifier(s) are upstream ofthe CM 112 _(X), how many coupling elements (amplifiers, splitters,directional couplers, etc.) are between the CMTS 102 and the CM 112_(X), GPS coordinates, and street address. In block 324, the CMTS 102assigns the CMs 112 ₁-112 ₅ to service groups based on their determinedlocations. Blocks 326 and 328 are substantially similar to blocks 308and 310, respectively, of FIG. 3A.

The locations of the CMs 112 ₁-112 ₅ may be determined by, for example,transmitting sounding signals into the network. In order to characterizethe channel with more precision, the channel sounding signal may be sentrepeatedly over an interval of time and the CMs may average multiplemeasurements over the time interval until they can resolve identifyingcharacteristics in the signal which indicate, for example, how manybranch amplifiers and/or other coupling elements that the signaltraveled through to reach the CM. In another example implementation, theCMTS may communicate with a server that stores subscriber informationthat associates the CMs with their geographic location (e.g., streetaddress).

While FIGS. 3A and 3B depict SNR profiles and location as two separatebases on which to assign CMs to service groups, the two may be used incombination.

FIGS. 4A and 4B illustrate the network of FIG. 1, with differentgroupings of CMs based on one or both of: measured performance metric(s)and location within the HFC network.

In the example of FIG. 4A, CMs 112 ₁, 112 ₄, and 112 ₅ are assigned toservice group 402 and CMs 112 ₂ and 112 ₃ are assigned to service group404. The assignment of FIG. 4A may result from, for example, assigningCMs based on the number of coupling elements between the CMTS 102 andthe CMs—four each for CMs 112 ₁, 112 ₄, and 112 ₅; five each for CMs 112₂ and 112 ₃. The number of coupling elements may be determined based on,for example, measured performance metrics (e.g., SNR profile) of the CMsand/or address or GPS information associated with the CMs.Alternatively, the assignment of FIG. 3A may result from, for example,assigning the CMs to service groups based directly on their respectivemeasured performance metric(s) (e.g., the extra device in the pathbetween CMTS 102 and CMs 111 ₂ and 112 ₃ may cause CMs 112 ₂ and 112 ₃to have significantly poorer SNR).

In the example of FIG. 4B, CMs 112 ₁, 112 ₂, and 112 ₃ are assigned toservice group 406 and CMs 112 ₄ and 112 ₅ are assigned to service group408. The assignment of FIG. 4B may result from, for example, assigningCMs based on which trunk amplifiers are downstream of the CMs.Alternatively, the assignment of FIG. 3A may result from, for example,assigning the CMs to service groups based directly on their respectivemeasured performance metric(s) (e.g., the distance between CMTS 102 andCMs 112 ₄ and 112 ₅ may be substantially greater than the distancebetween the CMTS 102 and the CMs 112 ₁, 112 ₂, and 112 ₃, thus resultingin poorer SNR in CMs 112 ₄ and 112 ₅).

Grouping CMs according to which trunk or distribution amplifiers areupstream of them may enable duty cycling power branch and/ordistribution amplifiers. For example, when a CM in service group 406 isthe talker, the upstream path through amplifier 1062 may be disabledsuch that noise from group 408 does not interfere with transmissionsfrom the talker of service group 406. Grouping CMs according to whichtrunk or distribution amplifier(s) serve(s) them may enable using moreefficient physical layer parameters. For example, where there is arelatively long distance of cable between amplifier 106 ₁ and 106 ₂ butrelatively short distance of cable between amplifiers 106 ₁ and 106 ₃,grouping the CMs by geography/distance to the CMTS may enable a lowertransmit power to be used by the CMTS 102 when talking to service group406 as compared to when talking to service group 408.

Other embodiments of the invention may provide a non-transitory computerreadable medium and/or storage medium, and/or a non-transitory machinereadable medium and/or storage medium, having stored thereon, a machinecode and/or a computer program having at least one code sectionexecutable by a machine and/or a computer, thereby causing the machineand/or computer to perform processes described.

Accordingly, the present invention may be realized in hardware,software, or a combination of hardware and software. The presentinvention may be realized in a centralized fashion in at least onecomputing system, or in a distributed fashion where different elementsare spread across several interconnected computing systems. Any kind ofcomputing system or other apparatus adapted for carrying out the methodsdescribed herein is suited. A typical combination of hardware andsoftware may be a general-purpose computing system with a program orother code that, when being loaded and executed, controls the computingsystem such that it carries out the methods described herein. Anothertypical implementation may comprise an application specific integratedcircuit or chip.

The present invention may also be embedded in a computer programproduct, which comprises all the features enabling the implementation ofthe methods described herein, and which when loaded in a computer systemis able to carry out these methods. Computer program in the presentcontext means any expression, in any language, code or notation, of aset of instructions intended to cause a system having an informationprocessing capability to perform a particular function either directlyor after either or both of the following: a) conversion to anotherlanguage, code or notation; b) reproduction in a different materialform.

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.

What is claimed is:
 1. A method comprising: determining, by a cablemodem termination system (CMTS), for a plurality of cable modems servedby said CMTS, a corresponding plurality of signal-to-noise ratio (SNR)related metrics comprising SNR versus frequency profiles; assigning, bysaid CMTS, said plurality of cable modems among a plurality of servicegroups based on said plurality of SNR-related metrics; generating, bysaid CMTS for each one of said plurality of service groups, a compositeSNR-related metric based on a portion of said plurality of SNR-relatedmetrics corresponding to said one of said plurality of service groups;selecting, by said CMTS, physical layer communication parameters to beused for communicating with said one of said plurality of service groupsbased on said composite SNR-related metric; and communicating, by saidCMTS, with a portion of said plurality of cable modems corresponding tosaid one of said plurality of service groups using said selectedphysical layer communication parameters, wherein said composite SNRrelated metric is a worst-case SNR versus frequency profile for said oneof said plurality of service groups.
 2. The method of claim 1, whereinsaid physical layer communication parameters include one or more of:transmit power, receive sensitivity, timeslot duration, modulation type,modulation order, forward error correction (FEC) type, and FEC coderate.
 3. The method of claim 1, wherein said CMTS uses orthogonalfrequency division multiplexing (OFDM) over a plurality of subcarriersfor said communicating.
 4. The method of claim 3, comprising selecting,by said CMTS, said physical layer communication parameters on aper-OFDM-subcarrier basis.
 5. The method of claim 4, wherein saidphysical layer communication parameters include one or both of: which ofsaid OFDM subcarriers to use for transmission to said CMTS, and which ofsaid OFDM subcarriers to use for reception of information from saidCMTS.
 6. The method of claim 1, wherein: said plurality of servicegroups comprises a first service group and a second service group; saidfirst service group has a first composite SNR versus frequency profile,said second service group has a second composite SNR versus frequencyprofile, and a third cable modem has a particular SNR versus frequencyprofile; and said assigning said plurality of cable modems among saidplurality of service groups comprises: assigning said third cable modemto said first service group if said particular SNR versus frequencyprofile is more similar to said first composite SNR versus frequencyprofile than to said second composite SNR versus frequency profile; andassigning said third cable modem to said second service group if saidparticular SNR versus frequency profile is more similar to said secondcomposite SNR versus frequency profile than to said first composite SNRversus frequency profile.
 7. The method of claim 1, comprising assigningsaid plurality of cable modems among said plurality of service groupsbased on distances between said CMTS and said plurality of cable modems.8. The method of claim 1, comprising assigning any particular one ofsaid plurality of cable modems to one of said plurality of servicegroups based on which one or more of a plurality of branch amplifiersare upstream of said one of said plurality of cable modems.
 9. Themethod of claim 1, wherein said determining said plurality ofSNR-related metrics comprises: transmitting a probe message to each saidplurality of cable modems, said probe message comprising instructionsfor measuring a metric and reporting said measured metric back to saidCMTS; and receiving a metric reporting message from each of saidplurality of cable modems.
 10. A system comprising: circuitry for use ina cable modem termination system (CMTS), said circuitry comprising anetwork interface and a processor wherein: said processor is configuredto determine, for a plurality of cable modems served by said CMTS, acorresponding plurality of signal-to-noise ratio (SNR) related metricscomprising SNR versus frequency profiles; said processor is configuredto assign said plurality of cable modems among a plurality of servicegroups based on said plurality of SNR-related metrics; said processor isconfigured to generate, for each one of said plurality of servicegroups, a composite SNR-related metric based on a portion of saidplurality of SNR-related metrics corresponding to said one of saidplurality of service groups; said processor is configured to selectphysical layer communication parameters to be used for communicatingwith said one of said plurality of service groups based on saidcomposite SNR-related metric; and said network interface is configuredto communicate with a portion of said plurality of cable modemscorresponding to said one of said plurality of service groups using theselected physical layer communication parameters, wherein said compositeSNR related metric is a worst-case SNR versus frequency profile for saidone of said plurality of service groups.
 11. The system of claim 10,wherein said physical layer communication parameters include one or moreof: transmit power, receive sensitivity, timeslot duration, modulationtype, modulation order, forward error correction (FEC) type, and FECcode rate.
 12. The system of claim 10, wherein said network interfaceand said plurality of cable modems are configured to communicate usingorthogonal frequency division multiplexing (OFDM) over a plurality ofsubcarriers.
 13. The system of claim 12, wherein said network interfaceis configured such that said physical layer communication parameters areconfigurable on a per-OFDM-subcarrier basis.
 14. The system of claim 12,wherein said physical layer communication parameters include one or bothof: which of said OFDM subcarriers to use for transmission to said CMTS,and which of said OFDM subcarriers to use for reception of informationfrom said CMTS.
 15. The system of claim 10, wherein: said plurality ofservice groups comprises a first service group and a second servicegroup; said first service group has a first composite SNR versusfrequency profile, said second service group has a second composite SNRversus frequency profile, and a third cable modem has a particular SNRversus frequency profile; said assignment of said plurality of cablemodems among said plurality of service groups comprises: assignment ofsaid third cable modem to said first service group if said particularSNR versus frequency profile is more similar to said first composite SNRversus frequency profile than to said second composite SNR versusfrequency profile; and assignment of said third cable modem to saidsecond service group if said particular SNR versus frequency profile ismore similar to said second composite SNR versus frequency profile thanto said first composite SNR versus frequency profile.
 16. The system ofclaim 10, wherein said processor is configured to assign said pluralityof cable modems among said plurality of service groups based ondistances between said CMTS and said plurality of cable modems.
 17. Thesystem of claim 10, wherein said processor is configured to assign saidplurality of cable modems among said plurality of service groups basedon a branch further branch amplifier that serves each of said pluralityof cable modems.
 18. The system of claim 10, wherein said determinationof said plurality of SNR-related metrics comprises: transmission, viasaid network interface, of a probe message to each said plurality ofcable modems, said probe message comprising instructions for measuring ametric and reporting said measured metric back to said CMTS; andreception, via said network interface of said CMTS, of a metricreporting message from each of said plurality of cable modems.